1. Field of the Invention
The present invention relates to a micrometric separator for the classification of mixtures of solid particulate materials, in which a flow of fluid, preferably air, has the function of conveying the particulate material, inducing it to slide along appropriate retainer walls in such a way that, on account of the different physical properties of the particles, there occurs a separation thereof according to particle size. This particle-size separation (i.e. the granulometric separation) is of particular importance in the field of organic substances in powder form, because it enables mixtures of materials to be obtained with a specific particle-size (granulometry), having organoleptic characteristics that can be decided a priori in the course of classification. Also in the context of the mixtures of inorganic materials, the separation of mixtures with homogeneous particle-size is of great importance, for example in the field of materials for the building sector.
2. Discussion of Related Art
Among the various types of micrometric classifiers, pneumatic separators, i.e., ones with forced fluid flow for the drawing-along (entrainment) of the material, are commonly used, both on account of their efficiency, and on account of the relative simplicity of use. In the context of the above-mentioned pneumatic separators, classifiers of particulate material are known that are made up of a plurality of cyclone devices set in series, in which the mixture of materials is introduced into a container having the shape of a truncated cone with a vertical axis (cyclone), usually in a direction tangential to the side walls of the latter, so as to obtain a centrifugal vortical flow of the material to be separated. The particles, which are induced, in their circular motion, to slide along the side walls of the container, are thus substantially subject to the centrifugal force resulting from the flow of conveying air, to the force of friction, in a direction opposite to the centrifugal force, which develops in the interaction of the material with the walls of the container themselves, and to the force of gravity. Inside the cyclone there is also present an ascending flow of air, which develops at the vertical axis of the cyclone itself.
The different kinetic energy which, by virtue of the above-mentioned forces, particles with different density and particle-size possess, brings about a separation of the material within the cyclone. The particles of large weight tend to drop along the walls and to deposit in a collection hopper. The collection hopper is set at the base of the container, which has the shape of a truncated cone. Finer particles, which are of small weight, tend to be drawn by the forced flow of air towards an outlet pipe, which is usually axial, of the cyclone itself. The geometry of the container having the shape of a truncated cone and the amount of flow of drawing air determine separation of particles that are of different particle-sizes (i.e. granulometry). Hence, by using in series cyclones presenting different characteristics and possibly varying the characteristics of the flow, a progressive classification of the particles is obtained.
The above separators, albeit of simple construction, are of large overall dimensions, tend to be very subject to wear, and prove far from sensitive to the finer granulometry of the material.
With the aim of increasing the efficiency of classification of centrifugal separators (cyclone separators) with tangential introduction of particulate matter, there have been proposed centrifugal-separation devices, in which the particulate material is introduced axially into a cylindrical container with a vertical axis so as to deposit on a disk, which is appropriately shaped and perforated and which is separated by gaps from the walls of the cylinder and is traversed by a forced flow of air. The kinetic energy exerted on the particles and the paths along which the latter are forced to move determine the separation of particulate matter of different size.
The above type of pneumatic separator, which is for example described in the patent No. EP 0.128.392 B1 in the name of the present applicant, achieves a high efficiency of separation, but is structurally complex and of difficult construction. In addition, it may be subject to wear and to jamming of the material to be classified.
A purpose of the present invention is to provide a separator for the classification of solid particulate materials which is extremely efficient as regards granulometric separation and at the same time is of simple construction.
Another purpose of the present invention is to provide a classifying separator for particulate matter that is not subject to jamming of the material during use and which can be regulated simply and precisely.
A purpose of the present invention is also to obtain a system or plant for the classification of solid particulate materials that is of simple construction, of high sensitivity to the finer particle-sizes (granulometry) of the particulate and affords ease of maintenance. A further purpose of the present invention is to provide a method for the separation of particulate materials that is particularly easy to implement and that presents a great effectiveness of classification.
The above and other purposes are achieved by the micrometric separator for the separation of solid particulate materials, by the system for the separation of solid particulate materials and by the method according to the present invention.